The present invention relates to an image sensing apparatus, and, more particularly, to an image sensing apparatus which switches between color image sensing and monochromatic image sensing.
An electronic still camera provides computer equipment with the image information of a three-dimensional object. The still camera includes an image sensor, a driver for the image sensor, and a signal processing circuit which generates an electrical signal of the object image in one screen picked up by the image sensor.
FIG. 1 is a schematic block diagram of a conventional electronic still camera 100, and FIG. 2 is a timing diagram for describing the operation of the camera 100 of FIG. 1. The still camera 100 includes an image sensor 1, a color separation filter 2, a lens 3, a driver 4, an analog processing circuit 5, an A/D convertor 6 and a digital processing circuit 7.
The image sensor 1 is preferably a charge-coupled device (CCD) image sensor and includes a plurality of light receiving pixels (picture elements), which are arranged in a matrix and accumulate an information charge by photoelectric conversion, and a plurality of shift registers which transfer the information charge accumulated in each light receiving pixel in a predetermined order. A plurality of the shift registers includes a plurality of vertical shift registers, which transfer the information charge in each column of the light receiving pixel, and a horizontal shift register which transfers the output of a plurality of the vertical shift registers. The color separation filter 2 has a plurality of segments mounted on the light receiving surface of the image sensor 1. The plurality of segments are formed by the three primary colors of light or their complementary color elements arranged in accordance with a predetermined rule. By using the color separation filter 2, each light receiving pixel is associated with a specific color component. The color separation filter 2 may also be formed as an on-chip filter by laminating a layer on the semiconductor image sensor 1. The lens 3 is arranged on the color separation filter 2 and guides the light from an object to the light receiving surface of the image sensor 1 via the color separation filter 2.
The driver 4 generates a vertical transfer clock xcfx86V, a horizontal transfer clock xcfx86H and a discharge clock xcfx86D for pulse-driving the image sensor 1 in accordance with an instruction from a timing control circuit 8. As shown in FIG. 2, after the information charge of the light receiving pixel is fully discharged in accordance with the discharge clock xcfx86D and a predetermined period L elapses, the information charge is transferred from each light receiving pixel to the corresponding vertical shift register in accordance with the vertical transfer clock xcfx86V. At this time, the information charge is transferred to the vertical direction in a unit of one line by a vertical shift register. The information charge from a vertical register is transferred to the horizontal direction every pixel by a horizontal shift register in accordance with the horizontal transfer clock xcfx86H. Thus the image information of one screen is successively output from the image sensor 1 in a unit of one line as an image signal A0(t).
The analog processing circuit 5 receives the image signal A0(t) from the image sensor 1, performs processing such as sample holding and level correction on an image signal, and generates a formatted analog image signal A1(t). The A/D convertor 6 receives an analog image signal A1(t) from the analog processing circuit 5 and converts the analog image signal A1(t) to digital image data D1(n) every pixel. The digital processing circuit 7 receives the digital image data D1(n) from the A/D convertor 6, performs processing such as color separation and matrix operation on the digital image data D1(n), and generates luminance data Y which represents luminance information and two types of chrominance data U and V which represent the chrominance information. The luminance data Y and the chrominance data U and V are transferred to a computer in units of one screen.
For example, the luminance data Y is generated by combining the three primary colors (red: R, green: G, and blue: B) of light generated by color separation at a ratio of 0.3 R+0.6 G+0.1 B. The chrominance data U and V are generated by subtracting the red component R and the blue component B from the luminance data Y.
The timing control circuit S controls each of the circuits 4 to 7 in accordance with a reference clock CK. For example, the timing control circuit 8 controls the driver 4 such that an accumulation time L of the information charge is set in accordance with the exposed state of the image sensor 1 and an image signal A0(t) having an appropriate level can be obtained. Further, the timing control circuit 8 sets the processing conditions of the analog and digital processing circuits 5 and 7 so that the processing of the analog and digital processing circuits 5 and 7 is synchronized with the operation of the image sensor 1.
The image information supplied to the computer also includes a monochromatic image of a document on which characters are written and graphics are drawn. Accordingly, it is preferable that an electronic still camera be provided with a color image sensing mode in which an object is photographed, and a monochromatic image sensing mode which generates an image representing only the light and shade of the object. The image sensing mode can be switched by changing the arithmetic operation processing of the digital processing circuit 7. The monochromatic image sensing mode is effective for improving resolution to preferentially process the luminance information. However, to obtain high resolution based on the image signal D1(t) generated using the color separation filter 2, complicated filtering processing must be performed on the separated color component data, which makes the circuit configuration of the digital processing circuit 7 complex.
It is an object of the present invention to provide an image sensing apparatus which switches between color image sensing and monochromatic image sensing without making the configuration of a digital processing circuit complex.
In one aspect of the present invention, an image sensing apparatus is provided that includes a solid-state image sensor having a plurality of light receiving elements which accumulate an information charge by photoelectric conversion. A color separation filter is arranged in front of the solid-state image sensor and has a plurality of filter segment groups. Each filter segment group corresponds to each of the plurality of light receiving elements, respectively and includes a first color filter segment having a first color selected from the three primary colors of light and second and third color filter segments having the complementary colors of the non-selected two of the three primary colors. A monochromatic filter is movably arranged between a position in an optical path to the plurality of light receiving elements and a position away from the optical path to the plurality of light receiving elements. The monochromatic filter has substantially the same first color as the first color filter segment. A driver transfers the information charge accumulated by the plurality of the light receiving elements in a predetermined order and drives the solid-state image sensor so as to output an image signal therefrom.
In another aspect of the present invention, an electronic camera is provided that includes an image sensor including a plurality of light receiving pixels that receive light irradiated on a surface of the image sensor. The image sensor accumulates an information charge by photoelectric conversion of the received light. A color separation filter is arranges adjacent to the image sensor. The color separation filter has a plurality of segments formed by at least three color components of light, such that each light receiving pixel is associated with a specific one of the at least three colors. A lens is arranged adjacent to the color separation filter for guiding light from an object to the image sensor by way of the color separation filter. The guided light travels along an optical path extending from beyond the lens to the image sensor. A monochromatic filter is located in the optical path. The monochromatic filter limits color components of the light irradiated on the image sensor. A combination of the color components of the color separation filter and the monochromatic filter is selected such that the color component passed by the monochomatic filter is also passed by the color separation filter. A signal processing circuit receives the information charge and generates luminance data and chrominance data. The processing circuit is operable in either a color image sensing mode or a monochrome image sensing mode.